Method for manufacturing and reoxidizing a TiN/Ta2O5/TiN capacitor

ABSTRACT

A method for manufacturing a TiN/Ta2O5/TiN capacitor, including the steps of forming a Ta 2 O 5  layer on a TiN support by a plasma-enhanced atomic layer deposition method, or PEALD; and submitting the obtained structure to an N 2 O plasma for a duration sufficient to oxidize the Ta 2 O 5  layer without oxidizing the TiN support.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the priority benefit of French patentapplication number 11/50923, filed on Feb. 4, 2011, entitled METHOD OFMANUFACTURING AND REOXIDIZING A TIN/TA2O5/TIN CAPACITOR, which is herebyincorporated by reference to the maximum extent allowable by law.

BACKGROUND

1. Technical Field

Embodiments relate to the manufacturing of a TiN/Ta₂O₅/TiN capacitor andmore specifically to a method for reoxidizing the Ta₂O₅ layer after itsforming on a TiN support.

2. Discussion of the Related Art

The use of TiN/Ta₂O₅/TiN-type capacitors has increased over the lastyears, especially on account of their compatibility with themanufacturing of the metallization levels of an integrated circuit andbecause, due to the high dielectric constant of Ta₂O₅, they can havehigh capacitances for small surface areas. Such capacitors are, forexample, used to form the capacitors of DRAM-type memory cells, of radiofrequency filters, or of analog-to-digital converters.

Among methods for forming such capacitors, a plasma enhanced atomiclayer deposition method has been provided to form the Ta₂O₅ layer, thismethod presently called PEALD.

This method comprises alternating phases of tantalum deposition from aprecursor, currently, the so-called TBTDET product, that is,tertbutylimido-tris-diethylamino tantalum, and phases of application ofan oxygen plasma. Then, an upper TiN electrode is deposited by anyadapted method.

Among the qualities which are expected from a capacitor, it isespecially desired for it to have as low a leakage current as possible,preferably below 10⁻⁷ A/cm². The dielectric relaxation factor is alsodesired to be reduced. This relaxation factor, FR, characterizes thecapacitance variation of a capacitor according to frequency and isdefined by relation FR=[C(1 kHz)−C(10 kHz)]/C. Thus, this factorcharacterizes the capacitance variation of a capacitor between anoperation at a 1-kilohertz frequency and an operation at a 10-kilohertzfrequency. Physically, this factor is linked to the presence of dipolesin the dielectric and to the relaxation time of these dipoles.

Various standards set the desired values of the relaxation factor.Present standards need for this relaxation factor to be, in percent,smaller than 0.2 for a capacitor operation at 25° C. and smaller than0.6 for a capacitor operation at 125° C.

To obtain such leakage current characteristics and the dielectricrelaxation factor, the applicant has provided:

all along the PEALD process, to limit the temperature within a rangefrom 200 to 250° C.,

during the steps of tantalum deposition from TBTDET, limiting thepartial TBTDET pressure within a range from 0.05 to 5 Pa, preferablyfrom 0.5 to 2 Pa, preferably on the order of 1 Pa to within 10%, and

during phases of application of an oxygen plasma, limiting the partialoxygen pressure within a range from 1 to 2,000 Pa, preferably from 10 to30 Pa, preferably to 25 Pa to within 10%.

The applicant has shown that this choice provides optimized results interms of leakage current and of dielectric relaxation factor.

After the steps of forming of the Ta₂O₅ layer on a TiN support, it canbe observed that there inevitably still remain defects, and especiallyoxygen vacancies.

To improve the state of the Ta₂O₅ layer, a reoxidizing is known to bedesirable at the end of the process.

However, experience shows that reoxidations performed up to now providevery inhomogeneous results and can even alter some characteristics,especially the leakage current or the dielectric relaxation factor ofthe finally-obtained capacitor. Further, in the case of the integrationof MIM (Metal-Insulator-Metal) structures at the level the interconnectsof a circuit, the processing temperature must be lower than 400° C., oreven lower than 350° C., to preserve the integrity of the interconnects.

There thus is a need to improve the reoxidizing process of a Ta₂O₅ layerin a capacitor of TiN/Ta₂O₅/TiN type.

SUMMARY OF THE INVENTION

An embodiment provides a method for reoxidizing a Ta₂O₅ layer formed ona TiN support which improves all the characteristics of thefinally-obtained capacitor and which especially decreases its leakagecurrent and its dielectric relaxation factor.

Another embodiment provides an improved capacitor.

Thus, an embodiment provides a method for manufacturing a TiN/Ta₂O₅/TiNcapacitor, comprising the steps of:

forming a Ta₂O₅ layer on a TiN support by a plasma-enhanced atomic layerdeposition method, or PEALD; and

submitting the obtained structure to an N₂O plasma for a durationsufficient to oxidize the Ta₂O₅ layer without oxidizing the TiN support.

According to an embodiment, to determine said sufficient duration,successive trials are performed and cuttings through the Ta₂O₅/TiNstructure and analyses of the composition of the interface are carriedout, to determine the processing duration after which the entire Ta₂O₅layer is reoxidized while the TiN support and the TiN/Ta₂O₅ interfaceare untouched.

According to an embodiment, during the application of the N₂O plasma,the substrate temperature is maintained between 300 and 400° C.

According to an embodiment, the substrate temperature is maintainedwithin the range from 370 to 390° C.

According to an embodiment, during the plasma oxidation, the partial N₂Opressure is maintained between 10 and 3,000 Pa.

According to an embodiment, during the plasma oxidation, the partial N₂Opressure is maintained between 400 and 600 Pa.

An embodiment provides a TiN/Ta₂O₅/TiN capacitor wherein the interfacearea between the TiN support layer and the Ta₂O₅ layer has a thicknesssmaller than 2 nm.

The foregoing and other objects, features, and advantages will bediscussed in detail in the following non-limiting description ofspecific embodiments in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a Ta₂O₅ layer formed on a TiN support; and

FIG. 2 shows leakage currents of a TiN/Ta₂O₅/TiN capacitor before andafter reoxidation according to an embodiment.

DETAILED DESCRIPTION

FIG. 1 shows a Ta₂O₅ layer obtained by plasma-enhanced atomic layerdeposition on a TiN substrate. There inevitably exists an interfaceregion 1 between TiN and Ta₂O₅ comprising titanium, tantalum, oxygen,and nitrogen atoms in various proportions. The method of deposition ofTa₂O₅ on TiN will have been carried out to reduce the thickness of thislayer.

For the reoxidizing of the Ta₂O₅ layer, oxygen plasmas in the presenceof argon are generally used, but the reoxidizing effect due to oxygenradicals is generally counterbalanced by the presence of argon, which isa reducer for Ta₂O₅, and the number of oxygen vacancies present in thestructure is not notably decreased.

Pure oxygen plasmas thus should be used. The disadvantage of suchplasmas is that they are inevitably generated with a high power providedto the plasma generation system and that they are extremely active, thatis, very energetic radicals are generated. Thus, the penetration ofoxygen into the Ta₂O₅ layer is very difficult to control. Either thepenetration is not sufficient and the Ta₂O₅ layer is not sufficientlyprocessed across its entire thickness, or the oxygen penetrates all theway to the TiN layer. Conventionally, this had not been considered as adisadvantage since titanium oxides also form a dielectric of strongdielectric constant.

However, the applicant has observed that the presence of such titaniumoxides and the increase in the interface layer thickness would actuallyalter the characteristics of the leakage current and the dielectricrelaxation factor of the finally-obtained capacitor.

Thus, the applicant provides performing a reoxidation of the Ta₂O₅ layerwhich accurately stops at the level of the Ta₂O₅/TiN interface. Toachieve this result, the applicant provides using an oxidizing plasma,which is easier to produce with a low power provided to the plasmageneration system than a pure oxygen plasma. For this purpose, theapplicant provides using a N₂O plasma which is much less aggressive thana pure O₂ plasma. Thus, the penetration of oxygen into the Ta₂O₅ layeris controllable (from 5 to 120 seconds for a layer of a 50-nmthickness). The plasma oxidation step can then be stopped when theTa₂O₅/TiN limit has been reached.

In practice, to set the machine, successive trials will be carried outand cuttings through the Ta₂O₅/TiN structures and analyses of theinterface composition will be performed. The time at which then entireTa₂O₅ is reoxidized TiN while the TiN layer and the TiN/Ta₂O₅ interfaceare still untouched can thus be determined. Once this time has beendetermined, the machine will be set to operate according to the durationresulting from the previous trials.

FIG. 2 shows the leakage current in amperes per cm² according to theapplied electric field in MV/cm for a Ta₂O₅ layer on a TiN substrate.Curve 20 shows the leakage current density before reoxidation and curve22 shows the leakage current density after reoxidation. The leakagecurrent density remains lower than 10⁻⁷ A/cm² in the currently-usedelectric field range, from −1 to +1 MV/cm. Further, the applicant hasobserved that the dielectric relaxation factor, after a reoxidationprocessing such as described hereabove, is at least as small as beforethe processing.

A specific embodiment of the reoxidation process comprises using asubstrate temperature from 300 to 400° C., preferably close to 380° C.to within 5%. The pressure of pure N₂O ranges from 10 to 3,000 Pa, forexample from 400 to 600 Pa, preferably 500 Pa to within 10%. The powerof the plasma is maintained at its minimum value to obtain an ionizingof plasma gases.

The use of the disclosed method causes that the thickness of theinterface layer between Ta₂O₅ and TiN is smaller than 2 nm, after thereoxidation processing. Thus, embodiments aim at the product formed of aTiN/Ta₂O₅/TiN capacitor in which the thickness of the interface layerbetween Ta₂O₅ and TiN is smaller than 2 nm, after the reoxidationprocessing.

Of course, the present invention is likely to have various alterations,modifications, and improvements which will readily occur to thoseskilled in the art. Such alterations, modifications, and improvementsare intended to be part of this disclosure, and are intended to bewithin the spirit and the scope of the present invention. Accordingly,the foregoing description is by way of example only and is not intendedto be limiting. The present invention is limited only as defined in thefollowing claims and the equivalents thereto.

What is claimed is:
 1. A method for manufacturing a TiN/Ta₂O₅/TiNcapacitor, comprising the steps of: forming a Ta₂O₅ layer on a TiNsupport by a plasma-enhanced atomic layer deposition method, or PEALD;and submitting the obtained structure to an N₂O plasma for a durationsufficient to oxidize the Ta₂O₅ layer without oxidizing the TiN support.2. The method of claim 1, wherein, to determine said sufficientduration, successive trials are performed and cuttings through theTa₂O₅/TiN structure and analyses of the composition of the interface arecarried out, to determine the processing duration after which the entireTa₂O₅ layer is reoxidized while the TiN support and the TiN/Ta₂O₅interface are untouched.
 3. The method of claim 1, wherein, during theapplication of the N₂O plasma, the substrate temperature is maintainedbetween 300 and 400° C.
 4. The method of claim 3, wherein the substratetemperature is maintained within the range from 370 to 390° C.
 5. Themethod of claim 1, wherein, during the plasma oxidation, the partial N₂Opressure is maintained between 10 and 3,000 Pa.
 6. The method of claim5, wherein, during the plasma oxidation, the partial N₂O pressure ismaintained between 400 and 600 Pa.
 7. A TiN/Ta₂O₅/TiN capacitor whereinthe interface area between the TiN support layer and the Ta₂O₅ layer hasa thickness smaller than 2 nm.